This invention is directed to curable high modulus epoxy reaction injection molding (RIM) compositions. The invention further relates to the manufacture of molded articles by reaction injection molding of catalyzed epoxy-polyamine compositions.
The use of urethane technology in RIM systems is well-known. In RIM technology the mixed urethane foam ingredients are injected into a mold cavity through a runner and a gate at low pressure, usually about 20 psi, where they react quickly to produce molded articles. Large parts can thusly be produced very quickly at relatively low mold pressures. Such elastomers normally comprise the reaction product of an aromatic polyisocyanate, a polyol and a chain extending agent.
Molding compositions of epoxy resins on the other hand are usually prepared by placing an epoxy composition comprising an epoxy resin and curing agent in a suitable mold, with or without reinforcement, and curing the composition under pressure and elevated temperature. These cured epoxy compositions exhibit good physical and chemical properties. It would be desirable; however, to be able to produce cured articles faster from epoxy compositions which exhibit physical and mechanical properties which are equal or superior to standard casting resins.
U.S. Pat. No. 3,492,269 is directed to a process for hardening epoxy resins using certain inorganic metal salt accelerators such as NaCl or NaBr, for the curing of said epoxy resins. These cured compositions cannot be used in RIM applications because of the relatively slow gel times. See, for example, Example 3 wherein gel times are in excess of 32 minutes. Further, although oxygenated organic solvents are disclosed as solvents for the metal salts, their use is said to be generally unnecessary.
An epoxy composition has now been found that exhibits a high modulus (ca 400,000 psi) and high strength (ca 10,000 psi) when produced via RIM techniques.